244
HEAVY MACHINERY
and erect the machinery, but no contractor will accept responsibility for the
foundations which are built to his drawings, as he cannot be expected to be
familiar with local conditions, or the peculiarities of the subsoil.
The datum line, or level from which all vertical dimensions are taken,
is usually the finished engine-room floor-level, and the foundation-block
height is carried up till, with an allownace of i in. to 2 in. for packing plates
Fig. I.-—-2O,ooo-kw» Turbo-alternator in Course of Erection, showing bottom half of Turbine Cylinder
in position, with Condenser and Valve Chest coupled up
under the bedplates, the top of the latter is at the required height with refer-
ence to the datum level. In some cases it is becoming the practice to build
short pieces of H-girders into the top of the foundation block to support the
bedplate; these girders are spaced every 3 ft. or so, and are carefully levelled
so as to present a smooth metal surface on which to level up the bedplates.
Where provision has to be made in the foundation block for foundation
bolts, it is advisable to make the holes big enough to allow at least 2 in.
lateral movement of the bolt in every direction; this allowance will take
care of any inaccuracies between the drawings of the bedplate and the actual